[Interest] Windows segfault, but not on Linux

[William Hallatt]

This is a very interesting angle to consider, thanks.  I do not personally
fire up multiple threads for this application...but my Ubuntu box has a
single CPU whereas the Windows machine I am trying to run it on has
8...mmm....


On 21 November 2013 12:36, Konrad Rosenbaum <konrad at silmor.de> wrote:

>  Hint: if your code is multi-threaded, behavior is radically different on
> Linux and Windows:
>
>
>
> * which thread runs first differs on single-CPU (and sometimes multi-CPU)
> systems
>
>
>
> * creating threads takes slightly longer on Windows, which may change some
> timing in accessing variables during thread startup
>
>
>
> * Windows has no strong CPU-Core-Bias, meaning threads switch between
> cores much more often, causing subtle differences in delays
>
>
>
> Hint 2: never assume something as innocuous as var++ is an atomic
> operation unless it is protected by a Mutex! My most recent hard-to-fix
> on-Windows-only crash was a race between refcnt++ and refcnt-- in a library
> that I didn't even write myself (libtcl).
>
>
>
> You can catch these by sifting through tons of false positives of the drd
> and helgrind tools of valgrind (you can filter out anything that is caused
> by QMutex and QSemaphore as false positives).
>
>
>
>
>
>
>
> Konrad
>
>
>
> On Thursday, Thursday 21 November 2013 at 10:12, William Hallatt wrote:
>
> > Thanks for the input!
>
> >
>
> > I have run it through valgrind before and didn't pick up anything weird,
>
> > but I think I will have to investigate this route more thoroughly (I
> admit
>
> > to doing some nasty raw pointer work with this guy, but the fact that it
>
> > ran so smoothly on Linux made me think I had nailed all the issues).
>
> >
>
> > Any amazing settings/valgrind options you prefer when valgrinding with
>
> > QtCreator (or command line)?
>
> >
>
> > PS Bo...I agree with you re system bugs, I am pretty sure the issue is on
>
> > my side, but now to find it! :D
>
> >
>
> > On 21 November 2013 10:19, Koehne Kai <Kai.Koehne at digia.com> wrote:
>
> > > > -----Original Message-----
>
> > > > From: interest-bounces+kai.koehne=digia.com at qt-project.org
>
> > > > [mailto:interest-bounces+kai.koehne=digia.com at qt-project.org] On
> Behalf
>
> > >
>
> > > Of
>
> > >
>
> > > > Bo Thorsen
>
> > > > Sent: Thursday, November 21, 2013 7:43 AM
>
> > > > To: interest at qt-project.org
>
> > > > Subject: Re: [Interest] Windows segfault, but not on Linux
>
> > > >
>
> > > > Hi William,
>
> > > >
>
> > > > Sounds like you have quite a nightmare of a bug there.
>
> > > >
>
> > > > I don't have a solution for you, but I can tell you my starting
> points
>
> > >
>
> > > for trying to
>
> > >
>
> > > > figure this one out.
>
> > > >
>
> > > > First is *always* this one: Have you run your application in
> valgrind?
>
> > >
>
> > > I'd start with that too, and here's why: Such 'weird' errors in
>
> > > seemingly unrelated code paths are often enough a sign of a memory
>
> > > corruption going on ... i.e. you're writing to invalid pointers etc
>
> > > somewhere else in your code.
>
> > >
>
> > > Regards
>
> > >
>
> > > Kai
>
> > > _______________________________________________
>
> > > Interest mailing list
>
> > > Interest at qt-project.org
>
> > > http://lists.qt-project.org/mailman/listinfo/interest
>
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